99cc Predator HF Build

Have a Pedator on the way to "mock up" our drive. I will remove the 79 CC from one of our test bikes and install the 99 CC and let everyone know the difference in the near future. Will need to wait for some better weather before I can test it.
I am very interested in seeing the "Worksman" project and how everything fits.

Have fun,

Hi. Excuse me, on the Q-Matic, if the clutch on the reduction side of the gear box engages, I'm guessing, at around 1300 rpm, then would the gear box ratio have to be changed from 2.7:1 for the 50cc HS to about 1.5:1 for the 99cc HF Predator engine so that the 99cc four stroke is not at near maximum rpm's when the clutch begins to engage? Am I right about this? Thankyou.

Hi Zean,


The drives used on low RPM motors [B & S, Cushman, Tech, Clinton, HF, Lifan, etc] are shipped with a 11.55 X 1 ratio. Drives for high RPM motors [HS, Honda, etc] are shipped with the 15.48 X 1 ratio.

The low RPM motor drives also use the AX series belt instead of the "15" series wedge belt. Using the wider belt and different primary pulley the primary ratio is 2.0638 X 1. It is important to note the Max Torque clutch operates much smoother than the "weed eater" style units and goes through the "ticking" cycle prior to enguagement. This means a much smoother transistion from minor slipping to total lock.

As many have found out moving the clutch to the rear and spinning it much slower than the crankshaft speed transfers more power to the rear wheel, as the motor doesn't waste power spinning the clutch at a higher speed. Moving the clutch to the rear also makes the drive system much thinner, and putting bearings on both sides of the clutch "buffer" a lot of the vibration of the clutch weights.

Have fun,

Hey Quinton. Are the clutches modified to have a slower engagment speed when they're mounted on the jackshaft , or does the engine spin up much more rpms than normaly used to engage an engine mounted clutch?

Hi. Thankyou for the insightful response. I really appreciate it. A different primary pulley is used to change the ratio of the Q-matic to 2.1 X 1 for the 99cc HF, and do we use a secondary pulley with a different groove for the wider AX series belt? I'm sorry about the twenty questions. Thankyou.

Hi. I'm sorry Quenton Guenther, I had to read your response three or four times before I understood that you have available two Q-Matic transmissions:1). with the drives used on low RPM motors and 2). drives for high RPM motors. I used to think that the Q-Matic is shipped with the 15.48 X 1 ratio then the customer made the appropriate changes to the drives if the transmission is being attached to a low RPM motor like the 99cc HF. Thanks again.

Hi wayne z,

The ratio is altered in the primary ratio by increasing the primary pulley and the clutch remains the same as the stock Q-Matic. We also increase the belt width with AX series belt which even alters the ratio more to spin the secondary clutch faster.

The great part about the Max Torque clutch is that it starts to enguage [called "ticking"] and gradually slides into total lock, whereas most other clutches hook up quickly. The Max Torque clutch allows using better ratios for "cruising speeds" with out winding the motor tight, and is the best choice for low RPM motors than need ratios nearer 12 x 1.

BTW all our pulleys are made to run 3/8", 15" series, 4L, and AX series belts.

Hope this information is helpful.

Have fun,

cory151 said:

Hey Quenton,

What mile per hour do you estimate I can hit with your trans and a 56 tooth rear sprocket? Just curious ( I won't hold you to it).

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I'm gonna guesstimate 37-38mph if that engine will rev to 6,000rpm. It should pull pretty strong and climb hills fairly well too.

cory151 said:

Well thats more than enough for me.

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That's plenty Bro, as you know. Can't wait to see this come together, it will be a nice ride! I can see your Morini collecting dust when you finish this build lol.

cory151 said:

Yeah I thought Id like a fast bike but cruising is more what i like day to day.

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Oh it'll be fast.....pushin close to 50mph on the downhills It will also be an awesome daily cruiser that's reliable......

cory151 said:

What did you use for crank extensions on your HF build? I seem to recall the motor was mounted decently high on that build so it may not have been needed.

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At first I installed the SBP cartridge BB w/206mm spindle. I needed a little more clearance when the engine was running and the CVT engaged so I used the wide kit and adapter from Bicycle-engines.com. No issues now and my engine is 14" wide from outside of CVT cover, to the outside of the re-coil cover.

Hi. Excuse me. The 99cc HF engine runs at 6000 rpm after the govenor is removed then you increase the jet size, add a free flow air filter and less restrictive exhaust? Do you have to install the high performance connecting rod so the piston or the original rod doesn't come off? Is it safe to run an engine 2000 or 2100rpm more than the factory set it at? I hope these questions are relevant, or is the performance the priority? Thankyou.

I run mine up to 5000 pretty regularly , have over 600 miles on it now. I changed to an aftermarjet air filter, drilled the jet .003" larger, and have a 1/2" conduit x 30" straight pipe with a 3/4" hotdog muffler on the end.

I am able to get the 79 CC motor to a little over 40 MPH without much effort with the Q-Matic. I suspect the 99 CC [only 17.8 CC larger] might make it to almost 45 in stock form.

Here is some information concerning the difference between the 79 CC and the 99 CC.

The bore & stroke of the 79 CC is 52 MM X 38 MM [80.7 CC], and the 99 CC is 56 MM X 40 MM [98.5 CC]. The foot print of the motors are very close with the 99 CC having a slightly smaller base. It only took a couple of minuites to make the motor fit on the mounting plate used on the 79 CC by using a small round file. The 79 has a footprint of 63 MM X 104 MM, whereas the 99 CC is 61.5 MM X 102 MM. These numbers are so close it doesn't take much effort to make either motor fit both the mounting plate and the Q-Matic drive. The side mounting holes are the same on both motors, meaning the Q-Matic drive is a direct bolt on system.

Because the test bike is blue, I removed the covers from the 79 CC and plan to exchange them with the black covers & rope starter from the 99 CC. I already exchanged the rope starter assembly and is an exact fit.

I plan to install the 99 CC in place of the 79 CC and use the same drive and ratios to see the actual difference between the motors. After the first test I will be installing the 2 speed proto type Q-Matic II to continue the testing phase.

I plan to offer the HF 79 [Carb approved for CA] for sale as we are done with the testing. I only logged 410 miles on the motor, and is like new [it will have the 99 CC black covers].

A little humor.......the 99 CC isn't legal in CA [not CARB approved], but the motor was shipped from CA to NC.

I just received the 99 CC yesterday and hope to check out carburetor size and main jet in the next couple of days. The carburetor has the #15 stamped on the top and I would guess it to be a 15 MM carburetor.

Have fun,

Hi Wayne,

We tested 5/8", 3/4", 7/8", and 1" flex pipe, and the 7/8" was by far the fastest. The 7/8" was almost 700 RPMs higher than the 5/8", and over 500 RPMs higher than the 1".
The difference between the 3/4" and the 7/8" was less than 350 RPMs.

Although we haven't tested the unit on a DYNO, we did use a local radar unit [thanks to the Dare county Sherriff], a GPS, mechanical speedometer [Whizzer], and a Tiny Tach in the process. At 11.55 X 1 ratio the difference between the 7/8" and the 5/8" pipe amounted to 4.5 MPH at top speed [40 MPH @ 6000 RPMs] [35.5 MPH @ 5300 RPMs].

The best test results were achieved with th 7/8" flex pipe @ 31.5" [not including any muffler, extension, tip, etc].

Have fun,